1. Field of the Invention
The present invention pertains generally to the use of a mixture of several charge transfer compounds of varying redox potential or the use of a single amphoteric organic charge transfer compound to produce optical devices and more particularly to the use of these organic charge transfer materials as a memory medium and switching mechanism for an optical system.
2. Description of the Contemporary and/or Prior Art
With the advent of the information revolution, recent research activities have focused on developing optical storage systems and optoelectronic switches. The interaction of laser light with matter has been intensely investigated because of its use in optical memory systems. Potentially, optical recording can produce information storage densities in excess of 100 million bits per square centimeter. Currently many optical memory devices rely on crystalline phase transitions (J. Stuke, Journal of Non-Crystalline Solids, Vol. 4, (1970) or on photochemical hole burning (PHB) in which a laser pits the material in an effort to store data. An article entitled "Laser Marking on a Thin Organic Film" by J. J. Wrobel et al, Applied Physics Letter 40, (11) June 1, 1982, describes such a technique using a laser beam to burn holes in a thin organic film. Similarly, optical writing on blue sputtered iridium oxide films is reported by Mabosch et al in Applied Physics Letter 41 (1), July 1, 1982. This technique uses an optical writing mechanism to thermally induce dehydration at temperatures below the melting point of the optical medium. An article entitled "Light-induced Phenomena in Dye-polymer Systems" by V. Novotny et al, The Journal of Applied Physics 50 (3), March 1979, describes an optical marking process based on diffusion in a dye-polymer system.
The prior art optical storage systems have one overriding disadvantage--prior art optical medium is not erasable. As a result, optical storage technology has found little application in computer technology, which requires both read, write and erase functions.
U.S. Pat. No. 4,371,883 (entitled "Current Controlled Bistate Electrical Organic Thin Film Switching Device (TCNQ)", filed Mar. 14, 1980) and a pending U.S. patent application (entitled "Method of Fabricating a Current Controlled Bistate Electrical Organic Thin Film Switching Device (TCNQ)", filed June 7, 1982, Ser. No. 385,523) filed by Richard S. Potember, Theodore O. Poehler and Dwaine O. Cowan, disclose a class of organic charge transfer salts, such as CuTCNQ, which exhibit stable and reproducible bistate switching between an equilibrium, or first state, and a second state, in the presence of an applied electrical field. These references disclose that certain organic charge transfer salts will undergo a bistate reversible electrochemical topotactic redox reaction in the presence of an applied electric field. The electrical field causes the organic salt to switch from a first state to a second (i.e., bistate switching). A detectable impedance change occurs between the equilibrium, or first state, and the second state thereby allowing one to determine if a particular area is in the first or second state. In specific, an electrical field is applied across a thin film of CuTCNQ, or an equivalent organic charge transfer salt. When the applied electrical field exceeds a threshold value the impedance across the thin organic film will drop from a relatively high impedance to a relatively low impedance.
Two papers written by Richard S. Potember et al report that when the organic films is electrically switched, the second state has different optical properties from the equilibrium or first state: (1) "The Vibrational and X-ray Photoelectron Spectra of Semiconducting Copper-TCNQ Films" Chemica Scripta, Vol. 17, 219-221 (1981); and (2) "Electrical Switching and Memory Phenomena in Semiconducting Organic Thin Films" American Chemical Society Symposium Series No. 184 (1982). These articles describe infrared spectroscopic means and reference well known Raman spectroscopic techniques (S. Matsuzaki et al, "Raman Spectra of Conducting TCNQ Salts" Solid State Communications, Vol. 33, pp. 403-405, 1980) for determining if the CuTCNQ film, switched by an Ac or DC electric field is in the first or second state. Follow-up work reported by E. I. Kamitsos et al used Raman spectroscopic techniques to verify the electrochemical charge transfer equation described in the above-referenced articles which causes the CuTCNQ salt to switch from the first to second state: "Raman Study of the Mechanism of Electrical Switching in CuTCNQ films" Solid State Communications, Vol. 42, No. 8, pp. 561-565 (1982). These papers point out that spectroscopic means can be used to discern whether an area of CuTCNQ switched by an applied electrical field is in the first or second state.
Potember and Poehler, the present inventors, with Benson, filed a pending U.S. patent application entitled "Optical Storage and Switching Devices Using Organic Charge Transfer Salts", Ser. No. 464,771, filed Feb. 7, 1983, which is directed to a bistate optical switching device. They discovered that certain organic charge transfer salts will also experience two-state switching when exposed to optical radiation. It was discovered that when the optical radiation exceeds a certain threshold, the organic charge transfer salt switched from a first to a second state. Spectroscopic and other optical means are used to determine if a portion of the organic charge transfer material was in the first, equilibrium, or second switch state. That pending U.S. application describes certain optical devices used to store binary information--the first state can be represented by a "0", and the second or switched state can be represented by a "1". That application also describes certain optical and thermal means for switching the organic material from the switched state ("1" state) back to the equilibrium state ("0" state). However, the organic optical devices described in that pending application are two-state systems which can only store two bits of information on a particular area of the organic optical storage medium.